Laboratory methods necessary for detecting mutagenic substances in human body fluids were investigated and body fluids from individuals suspected to have occupational or other environmental exposure to mutagenic substances analyzed to confirm and partially quantitate such exposure. Compared with unexposed subjects, no evidence was found for increased levels of mutagenic substances in urine specimens from cases of or individuals at high risk for cancer of the bilharzial bladder, cases of cirrhosis or other disorders affecting hepatic function, or individuals occupationally exposed to agents used for cancer chemotherapy. In addition, no association was found between maternal smoking and the presence of mutagens in amniotic fluid. In the letter two studies, however, careful analysis of assay results suggested low levels of mutagenic activity in urine and amniotic fluid specimens from most subjects compared with solvent controls.